Multiblade fan



Get. 8, 1929. A. LAWRIE MULTIBLADE FAN Filed Aug. 10, 1927 Fig. 4

Invenfor:

AZexancZer Lavvm e M Affarney Patented Get. 8, 1929 MULTIBLADE FAN Application filed August 10, 1927, Serial No. 212,033, and. in Australia september 3, 1926.,

This invention is for improvements in fans and particularly'those known as multiblade fans in which a number of blades curved against the direction of rotation accelerate the velocity at which the air is discharged from 5 the periphery of the fan over and above the peripheral speed of the blades themselves.

In order that the invention may be better understood reference may be had to the accompanying drawings wherein Figure 1 is a part sectional elevation of a multiblade fanconstructed according to this invention, I

Figure 2 is a sectional end view of Figure 1, the right hand side being a section of the intake, and the left hand side the back end,

Figure 3 is a developed plan of a fan blade in accordance with this invention,

Figure 4 is a section of the intake end of the fan blade after bending,

Figure 5 is a section of the back end of the blade after bending.

Several types of multiblade fans are at present in use; one type has blades which, before being curved, are of rectangular shape, while in another type the blades are of right angled triangle shape before being curved. In the latter case the base of the triangle is at the back of the fan. Generally speaking the blades are curved forward at an angle of approximately forty-five degrees, and this angle of forward throw is in the direction of rotation.

It can be shown that where the blades are curved forward the efficiency is increased, as the radial velocity is reduced,and multiblade fans get this reduction in radial velocity by making the fans wide, thus giving-a blade much greater in length than in depth.- For instance, one design of fan has a blade depth of one sixteenth the diameter, the length of the blade being three fifths of the diameter; that is to say, the length of the blade is about nine times greater than the breadth or depth. 3

When the blades are made the same depth throughout their length, experiment has shown that a greater quantity of air passes through the inner part of the blades (the part furthest from the entrance) than is passed through the outer (the part nearest the entrance to the fan) This causes an unequal flow of air in the evase or hell shape of the fan, which sets up eddy currents and turbulence, the result of which is a consequent reduction of efficiency. 7 g I Attempts to overcome this reduction of efficiency have been made by making the blades much deeper at the inside than at the entrance end of the fan, and also by shaping the blades at the periphery so that the diameter of the fan mea'sured'at the blade tips was less at the inside than at the outside or entrance to the fan. Better distribution of the air was anticipated by the use of this form of blade. 7 I a My investigations in this'matter show that if this was so, it was due more to the resistance of the passage of the airthrough the fan being increased at the inside of the fan than to any other means, owing to the largely'increased area of the blade, and the smallpassageway to the blade tips at this point. My experiments led me to believe that the internal resistance of the fan could be reduced by shaping the blades so that the deepest part of the blade was at the entrance to the fan provided that it was not made too deep that the area of entrance would be diminished by 'too great anamount. i

It can thus be seenthat most experiments and improvementshave been made with the object of causing a more equal distribution of the air in passing through the fan blades. In accomplishing my invention 1 have endeavoured to overcome the same difiiculty, but I in addition have experimented as toanother factor, namely, the reduction of the internal resistance of the'fan. Although it is assumed in the foregoing that airflowing from the inside of the fanto' the periphery flows in a radial direction I have found that this is v not so, nor does it follow stream lines, but is whirled round inside the fanbefore reaching. the blades, the whirling action being greater the nearer the back of the fan is reached at any given radial distance from the centre of vthe fan. 1 i

\ To meet the air so that as little shock as possible takes place, the angle forward of the inside of the blade therefore has to vary be tween the entrance and back of the fan, since the velocity of the air is varied due to whirl between these two points. Where the air takes the same velocity as the blade itself, the part of the blade which meets the air should be pointing in a radial direction, so that no shock will take place. This occurs at the back end of the fan, while the greatest throw forward of the inside edge of the blade should also be at the entrance of the fan where the whirling action does not take place. In my invention this is done by having the blade deeper, or broader, at the entrance than at the back of the fan, so that with a constant forward throw of forty-five degrees,- or any other suitable angle, at the outer edge of the blade or periphery there is a varying angle of forward throw at the inside edge of from zero to forty-five degrees: that is to say, the inner part of the blade (the part at the back of the fan) takes the form of one eighth of a circle, and the outer part (that next the entrance) takes the form of one quarter of a circle of the same radius, when the forward throwof the outer edge of the blade, that is the periphery of the fan, is forty-five degrees.

The throw forward of the outer edge of the blade is not of so great importance, as with angles less than this good results would be attained, provided the varying inside angle of throw forward is maintained. The angle of throw forward of forty-five degrees is given with my blade, so that the necessary area of blade contact with the air should be acquired.

Referring now to Figures 1 and 2, which illustrate a multiblade fan in accordance with myinvention, a central boss A is keyed to a spindle B.- Spokes C radiate from the cen tral boss A and are secured to an angle iron ring D. Lugs F on the fan blades E are riveted to the angle iron ring D. An annular plate G is secured to the rim of the boss A, and has attached to it by lugs H the back ends of the fan blades E.

Referring to Figure 3 the preferred shape of plate from which the fan blade is shaped by being bent is shown; whilst Figures 4 and 5' show the relative sizes and curvature of the respective ends.

By way of example I wouldmention that good results have been obtained in a fan constructed according to this invention having an area of entrance of approximately twenty square feet by employing fifty-two blades whose area of contact with the air passing through the fan is about seventy-eight square feet; thearea of the blades to the area of entrance being in the ratio of about four to one.

The dimensionsspecifically given in the specification and drawings are those which I have used for illustration, and have found satisfactory. It will however be understood that in some cases I may vary these dimensions and obtain satisfactory results.

I claim 1. In multiblade fans curved blades which are deeper at the entrance than at the back of the fan, the back portion of each blade having the form of one eighth of a circle and the front portion having the form of a quarter circle of the same radius when the forward throw of the outer edge of the blade is forty-five degrees.

2. A multiblade fan comprising a central boss keyed to a spindle, spokes radiating from the boss to a ring atthe entrance to the fan, an annular plate on said boss, and curved blades of uniformly varying width whose radius of curvature is constant throughout their length and whose broad ends are rounded and secured to the said ring and whose narrow ends are secured to the said annular plate.

8. A fan comprising a plurality of curved blades being approximately twice as deep at the entrance as at the back of the fan and the sum of the forward throw angles of each blade at the periphery of thefan and the backward throw angle'of each blade at the inside of the fan at theentrance being 90.

In testimony whereof I aflix my signature.

ALEXANDER LAWRIE. 

